package Honor;

import java.util.Scanner;

public class Main1 {
    public static void main(String[] args) {
        Scanner cin=new Scanner(System.in);
        int n=cin.nextInt();
        if (n==1){
            System.out.println(1);
            return;
        }
        int[] dp=new int[n];
        dp[1]=2;
        dp[0]=1;
        for (int i = 2; i < n; i++) {
            dp[i]=dp[i-1]+dp[i-2];
        }
        int res=dp[n-1];
        for (int i = 0; i < n - 1; i++) {
            res+=(dp[i]*dp[n-i-1]);
        }
        System.out.println(res);
    }
}
